The present invention is directed to rebuilding hammers used in hammer mills for pulverizing coal and for breaking and grinding metal scrap, rock, masonry, refuse and the like. A worn hammer is rebuilt and returned to its original dimensions and weight by depositing a molten exothermic material on the worn surface. The exothermic material is selected so that the resultant weld is similar to Ni-Hard, a known wear-resistant metal.
In modern steel-making operations, coal is ground to a specific mesh size before coking so that coke of a proper quality for use in modern, high-throughput blast furnaces is available. Coal is pulverized in a hammer mill device, such as the Coalpactor, supplied by the Pennsylvania Crusher Corporation. In such a hammer mill, a large number of hammers, mounted on shafts, are rotated at high speed within a housing for grinding the coal to the desired size. The head of the hammer grinds the coal and, in turn, the grinding or wearing surface becomes worn and loses its effectiveness. When such a hammer loses about one-half inch of its length and about 10 per cent of its weight, the hammer is considered worn out and must be replaced.
In the past, worn hammers have been scrapped. Attempts to increase the life of hammers by conventional hardfacing techniques have not been successful.
In other types of hammer mills, with the hammers providing a crushing or grinding action, the wearing surface of the hammer becomes worn and less efficient, until finally it must be replaced.
In rebuilding worn-out hammers, the rebuilt hammer must closely match the weight and over-all length of a new hammer. Moreover, the cost of rebuilding must be less than the cost of a new hammer or it should provide a significantly longer effective lifetime.